1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices. More particularly, the present invention relates to a method of stripping a film from a wafer and which film had been formed on the wafer by chemical vapor deposition (CVD).
2. Description of the Related Art
When manufacturing a semiconductor device, various films such as an oxide film, a nitride film and a polysilicon film, are often formed on a wafer by chemical vapor deposition (CVD). The CVD process typically involves forming a film on both the wafer that is being processed and on a test wafer used for evaluating the quality of the film. The film formed on the test wafer is stripped therefrom after the quality test so that the test wafer can be reused.
In the conventional art, a wet etch method has been used for stripping the film formed on the test wafer. In this method (wafer stripping), the wafer is submersed in a wet bath filled with chemicals. In order to ensure that the film from the test wafer is completely stripped, the wafer is usually over-etched. Accordingly, the thickness of the wafer is reduced. As a result, the wafer becomes unusable after being stripped a number of times.
Another problem occurs when multiple layers must be formed on the test wafer. For example, in a process of producing a polysilicon film, the polysilicon is grown on an oxide film previously formed on the wafer. However, when stripping the polysilicon layer from the oxide layer, the oxide layer may be damaged or stripped. Accordingly, a new oxide film must be regrown before the test wafer can be reused. The repeated stripping and regrowing of the oxide layer is uneconomical and time consuming.
In an attempt to solve the above problems, a dry etching process using plasma to strip a wafer has been developed. However, this method can only be used to strip the wafers one by one. Thus, this method is also time consuming.